Analysis on the accelerating effects of open wound healing by chitin and chitosan were carried out in dogs. Two, square, full-thickness wounds of skin (2 × 2 cm2) were created on the each dog's both sides of dorsal midline at 0, 14, 21, and 24 days. In one dog, one wound (left side) was treated with chitin (chitin group) and the othor wound (right side) was not treated (control group). In another dog, one wound (left side) was treated with chitosan (chitosan group) and the other wound (right side) was not treated (control group). At 28 days after initial wounding, each wound site including surrounding tissue was taken for macroscopic and histological observations. Reepithelialization tended to be greater in chitin and chitosan groups than in the control group. However, when the scores of reepithelialization and granulation tissue were evaluated statistically, there was no significant differences in three groups during experimental period. Number of inflammatory cells was greater statistically in level in the control group than those in chitin and chitosan groups at 28 days after wounding. Many rete ridges were observed in the control group but very few in the another groups.